Develop Reference

Java - Convert From A Timezone Different From Local To UTC

So from all the posts I read about this issue (for example, Convert timestamp to UTC timezone).
I learn that a way to do this conversion is :
SimpleDateFormat dfmaputo = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss a");
dfmaputo.setTimeZone(TimeZone.getTimeZone("UTC"));
long unixtime = dfmaputo.parse(data.get(1)).getTime();
unixtime = unixtime / 1000;
output:
original date (Maputo Timezone) -- 11/5/2015 1:39:45 PM
unix timestamp in UTC --- 1446687585
data.get(1) is the string with the maputo datetime.
I don't understand why I'm not getting the UTC value. When I convert the unix timestamp, that I was expecting to be in UTC, I get the original datetime with Maputo Timezone.
Am I missing something?
Do I need to convert first to my local timezone and than to UTC?
EDIT: Solution
Calendar maputoDateTime = Calendar.getInstance(TimeZone.getTimeZone("Africa/Maputo"));
maputoDateTime.setTimeZone(TimeZone.getTimeZone("GMT"));
Long unixtimeGMT = maputoDateTime.getTimeInMillis() / 1000;
Instead of SimpleDateFormat I should use Calendar.
First I needed to set the input date's timezone (Africa/Maputo) and then set it to the one I needed (GMT). And only then I could get the correct unix timestamp.
Thanks to #BastiM reply in How to change TIMEZONE for a java.util.Calendar/Date
Thank you for your replies and help.

What if you add CAT timezone identifier to the end of string and formatter mask has z letter? If thats what you always get and source data does not give timezone value.
String sdt = "11/5/2015 11:39:45 PM CAT";
SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy hh:mm:ss a z", Locale.US);
Date dt = sdf.parse(sdt);
Calendar cal = Calendar.getInstance();
cal.setTimeInMillis(dt.getTime());
System.out.println(dt + ", utc=" + dt.getTime());
System.out.println(cal);

How to convert date strings from different TimeZones to Date object in one TimeZone

Im working on an RSS reader software. I get items with their pubDate (publish date) values as string, convert them to Date object, and put them to my DB. However, when I check my DB, I saw some interesting values such as the date of tomorrow.
I research this situation and found that it is about time zone value Z. For example when I get "Mon, 26 May 2014 21:24:29 -0500", it becomes "2014-05-27 05:24:29", the next day !
All I want is to get dates in any timezone and convert them to date in common timezone, such as my country's.
Here is my code :
public static String convert(String datestr) throws ParseException {
DateFormat formatter = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss zzz");
Date date = formatter.parse(datestr);
SimpleDateFormat resultFormatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
return resultFormatter.format(date);
}
And I use the method like that :
System.out.println(convert("Mon, 26 May 2014 21:24:29 -0500"));
The output is : 2014-05-27 05:24:29
Any idea ?

Since you haven't set a time zone, it's using your system's default.
Set a specific IANA time zone.
SimpleDateFormat resultFormatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
resultFormatter.setTimeZone(TimeZone.getTimeZone("America/New_York"));
return resultFormatter.format(date);

Looks like you passed a Date with timezone, but given a wrong format. If you are passing timezone like "-0500" you should rather use:
DateFormat formatter = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss Z");
Remember that the system will always display the date using the current, default timezone (TimeZone.getDefault()) unless you override it by:
resultFormatter.setTimeZone(...)

This is working as expected. The date is converted as per your system's timezone.
Check the UTC offset of your system and replace it in the sample date string and look at the output.
For e.g: India is UTC+5:30
String datestr="Mon, 26 May 2014 21:24:29 +0530";
output:
2014-05-26 21:24:29
Alternate solution
If you don't want to consider the timezone of the input date string then simply truncate this information and remove zzz from pattern as well as shown in below code:
String datestr = "Mon, 26 May 2014 21:24:29 -0530";
datestr = datestr.replaceAll("\\s[-+](\\d+)$", ""); // truncate the timezone info if not needed
DateFormat formatter = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss"); // remove zzz from the pattern
Date date = formatter.parse(datestr);
SimpleDateFormat resultFormatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
System.out.println(resultFormatter.format(date));

java date daylight saving

I just printed new Date() in my box, and it always returns the older time which corresponds to EST, however the date command in the box returns the exact time after moving to EDT, IS there anything that need to be done for the new Date() to return the exact date ? I do not want any alternate java commands, but want the Date to work as it is expected, Am I missing something ?
Thank you

try this:
DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
Calendar cal = Calendar.getInstance();
System.out.println(dateFormat.format(cal.getTime()));
Calendar.getInstance() gives you a Calendar object initialized with the current date / time, using the default Locale and TimeZone.

Hi the below code would be useful for your case.
SimpleDateFormat df = new SimpleDateFormat("dd MMM, yyyy HH:mm:ss z"); //Date format
df.setTimeZone(TimeZone.getTimeZone("EDT")); //set Timezone
df.format(new Date());
Thanks.

Converting datastamps to epoch (including GMT or UTC)

I am looking to convert timestamps into epoch (number of millisconds since 1970) - java.
I want an extensive parser - that supports both GMT/UTC and perheps other format.
For example:
new DateStamp("yyyy-MM-DD HH:mm:ss,ccc o").parse("2012-09-01 13:44:21222 GMT+2")
That is, I don't want to put in the actual format my self (GMT/UTC), but rather leave that for the parser.

You could use SimpleDateFormat:
DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss,S Z");
Date date = df.parse("2012-09-01 13:44:21,222 GMT+2:00");
long time = date.getTime(); // milliseconds since epoch
For ISO 8601 Time zone:
DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss,S Z");
Date date = df.parse("2012-09-01 13:44:21,222 +02");

Converting Epoch time to date string

I have seen this question asked multiple times and none of the answers seem to be what i need.
I have a long type variable which has an epoch time stored in it.
What i want to do is convert it to a String
for example if the epoch time stored was for today the final string would read:
17/03/2012
How would i to this?

Look into SimpleDateFormat
SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy");
sdf.format(new Date(myTimeAsLong));

You'd create a Date from the long - that's easy:
Date date = new Date(epochTime);
Note that epochTime here ought to be in milliseconds since the epoch - if you've got seconds since the epoch, multiply by 1000.
Then you'd create a SimpleDateFormat specifying the relevant pattern, culture and time zone. For example:
SimpleDateFormat format = new SimpleDateFormat("dd/MM/yyyy", Locale.US);
format.setTimeZone(...);
Then use that to format the date to a string:
String text = format.format(date);

Date date = new Date(String);
this is deprecated.
solution
Date date = new Date(1406178443 * 1000L);
DateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
format.setTimeZone(TimeZone.getTimeZone("Etc/UTC"));
String formatted = format.format(date);
make sure multiply by 1000L

If the method should be portable, better use the default (local time) TimeZone.getDefault():
String epochToIso8601(long time) {
String format = "yyyy-MM-dd HH:mm:ss";
SimpleDateFormat sdf = new SimpleDateFormat(format, Locale.getDefault());
sdf.setTimeZone(TimeZone.getDefault());
return sdf.format(new Date(time * 1000));
}

try this
Date date = new Date(1476126532838L);
DateFormat format = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss");
format.setTimeZone(TimeZone.getTimeZone("Etc/UTC"));
String formatted = format.format(date);
format.setTimeZone(TimeZone.getTimeZone("Asia/Colombo"));//your zone
formatted = format.format(date);
System.out.println(formatted);

Joda-Time
If by epoch time you meant a count of milliseconds since first moment of 1970 in UTC, then here is some example code using the Joda-Time library…
DateTimeZone timeZone = DateTimeZone.forID( "Europe/Paris" );
DateTime dateTime = new DateTime( yourMilliseconds, timeZone );
String output = DateTimeFormat.forStyle( "S-" ).withLocale( Locale.CANADA_FRENCH ).print( dateTime );
Other Epochs
That definition of epoch is common because of its use within Unix. But be aware that at least a couple dozen epoch definitions are used by various computer systems.

Time for someone to provide the modern answer (valid and recommended since 2014).
java.time
DateTimeFormatter formatter = DateTimeFormatter
.ofLocalizedDateTime(FormatStyle.LONG).withLocale(Locale.US);
String facebookTime = "1548410106047";
long fbt = Long.parseLong(facebookTime);
ZonedDateTime dateTime = Instant.ofEpochMilli(fbt).atZone(ZoneId.of("America/Indiana/Knox"));
System.out.println(dateTime.format(formatter));
The output is:
January 25, 2019 at 3:55:06 AM CST
If you wanted only the date and in a shorter format, use for example
DateTimeFormatter formatter = DateTimeFormatter
.ofLocalizedDate(FormatStyle.SHORT).withLocale(Locale.US);
1/25/19
Note how the snippet allows you to specify time zone, language (locale) and how long or short of a format you want.
Links
Oracle tutorial: Date Time explaining how to use java.time.
My example string was taken from this duplicate question

Try this...
sample Epoch timestamp is 1414492391238
Method:
public static String GetHumanReadableDate(long epochSec, String dateFormatStr) {
Date date = new Date(epochSec * 1000);
SimpleDateFormat format = new SimpleDateFormat(dateFormatStr,
Locale.getDefault());
return format.format(date);
}
Usability:
long timestamp = Long.parseLong(engTime) / 1000;
String engTime_ = GetHumanReadableDate(timestamp, "dd-MM-yyyy HH:mm:ss aa");
Result:
28-10-2014 16:03:11 pm

You need to be aware that epoch time in java is in milliseconds, while what you are converting may be in seconds. Ensure that both sides of the conversions are in milliseconds, and then you can fetch the date parameters from the Date object.

ArLiteDTMConv Utility help converting EPOUCH-UNIX Date-Time values, Form EPOUCH-UNIX-To-Date-format and Vise-Versa. You can set the result to a variable and then use the variable in your script or when passing as parameter or introduce in any DB criteria for both Window and Linux. (Download a zip file on this link)